Camshafts are used in internal combustion engines in order to actuate the gas exchange valves. The camshaft in an internal combustion engine includes a plurality of cams that engage cam followers (i.e. bucket tappets, finger levers or rocker arms). When the camshaft rotates, the cams lift the cam followers which in turn actuate gas exchange valves (intake, exhaust). The position and the shape of the cams define the opening period and amplitude as well as the opening and closing time of the gas exchange valves.
Concentric camshaft assemblies are also known in which separate intake and exhaust camshafts are concentrically arranged by providing a hollow outer camshaft in which an inner camshaft is located, with the inner camshaft cam lobes being rotatable on the outer camshaft, and connected through slots in the hollow outer camshaft to the inner camshaft. This allows the use of separate camshafts for intake and exhaust valve actuation within generally the same space required for a single camshaft.
A camshaft adjuster generally comprises a timing gear, which can be a chain wheel, a belt wheel or a gear wheel, and it is connected in fixed rotation to the crankshaft by a chain, a belt or a gear drive, and acts as an input to the adjuster. The adjuster also includes an output connection to the camshaft. An adjusting input is also provided which can be a hydraulic, pneumatic or even electric drive to adjust the output rotation relative to the input. Commonly used arrangements include adjusters that operate on the vane-cell principle.
A single cam phaser (SCP) is shown in U.S. Pat. No. 7,284,517. This SCP allows the timing of an inner camshaft and/or an outer camshaft to be adjusted relative to an engine crankshaft. This phaser uses a separate nose support piece that is separately supported in the first camshaft bearing in order to carry the axial load from the timing chain into the outer camshaft. This requires the nose support piece to have tight tolerances, so that the radial load imparted by the timing chain or belt into the timing gear or pulley on the phaser is transmitted from the phaser into the more structurally rigid outer shaft. If such a load is supported mainly by the inner camshaft, such as shown in the arrangements of DE 10 2005 014 680 A1 or DE 10 2006 024 794 A1, bending of the inner shaft may occur, thereby causing the inner and outer camshafts to bind, preventing intake versus exhaust valve timing adjustment. Additionally, the rear plate of U.S. Pat. No. 7,284,517 has to be assembled separately to the outer camshaft prior to the front plate then being assembled and connected to the inner camshaft. This further complicates engine assembly.
In one known hydraulically activated camshaft phaser which operates on the vane-cell principle, the front and rear covers of the phaser are separately attached to the inner and outer camshafts. The drawback of this arrangement is that durability is somewhat limited, and attaching the vanes to the covers is cumbersome. Due to having the vanes of the phaser connected to front and rear covers of the phaser, seals are required to retain the pressurized hydraulic fluid required to move the vanes of the phaser. Such seals are subject to wear and eventual failure. Further, such a multipart arrangement greatly increases labor and time in assembling this known SCP phaser as the engine is assembled. In assembling such a phaser to a concentric camshaft, the risk of internal phaser contamination is high. Furthermore the installation time and complexity are increased since multiple portions must be separately attached to multiple parts of the camshaft. This also requires more complex disassembly and assembly in the field for service.